Field of the Invention
The present invention relates to a manufacturing method of a PTC (Positive Temperature Coefficient) element using a polymer aqueous emulsion conductive composite, a PTC (Positive Temperature Coefficient) element manufactured by the manufacturing method, and a planar heating element including the same. More particularly, the invention relates to a PTC element manufactured by producing a conductive composite using a polymer aqueous emulsion without using an organic solvent and by coating or dipping a substrate with the conductive composite. The invention relates to a heating element manufactured by attaching an electrode to a PTC element and laminating an insulating covering material on. Since a temperature of the planar heating element is controlled while heating, safety of the heating element is significantly improved, and a separate temperature control device is unnecessary, which derives economic advantages.
Description of the Related Art
As a heating element which converts electric energy into thermal energy, there are a 1-dimensional heating element such as a resistance line and a 2-dimensional heating element such as a planar heating element. There are various devices used to secure safety by cutting off electric connection when a temperature of a heating element is overheated equal to or higher than a predetermined temperature, and one of them is a PTC (Positive Temperature Coefficient) element that prevent overheating by disabling electric connection by increase of resistance when overheating, and by allowing electric connection by decrease of resistance when cooling again. A technique of elements with such a function is a very important technique for securing safety.
As disclosed in “MANUFACTURING METHOD OF PTC ELEMENT AND OVERHEATING PREVENTING SYSTEM OF PLANAR HEATING ELEMENT USING THE SAME” (Korean Registered Patent Publication No. 10-1129251, Patent Literature 1) applied and registered by the inventor of the invention, there is a compounding forming method of melting polymers in a high temperature, in a conventional manufacturing technique of a PTC element. That is, a technique of manufacturing a PTC element in a sheet shape by melting a mixture including polymers and a conductive agent at a high temperature higher than a melting point of polymers by 20° C. or higher was used.
A disadvantage of the compounding forming technique is that an energy cost is high as compared with a solution process of the invention to be described later since polymers have to be melted at a high temperature. In addition, since polymers are formed in a continuous shape in the sheet-shaped manufactured PTC element, resistance change characteristics having an influence on electric connection are significantly changed according to repeating of overheating and cooling of the heating element to be different from an initial state, and reversibility is significantly decreased as a disadvantage. That is, the characteristics of cutting off electric connection by increase of resistance when the heating element is overheated and a temperature thereof is raised, and allowing electric connection by decrease of resistance when the heating element is cooled have to be kept initial even in using for a long time, but there is a disadvantage that the characteristics deviate with the lapse of use time and it is difficult to actually apply them to a heating element in which overheating and cooling are repeated.
Meanwhile, in the conventional technique, manufacturing a PTC element includes (1) a step of melting and mixing a compounding composite of polymers and a conductive agent, (2) a step of forming electrodes on both faces of the composite, (3) a step of forming the electrode-formed composite to be a sheet with a thickness of 0.2 to 3 mm, (4) a step of irradiating the sheet with an electron beam with 10 to 320 Kev to be cross-linked, and (5) a step of annealing after the cross-linking, and economical efficiency is lowered since the manufacturing method goes through complicated and various steps.
As a conventional technique about a solution state of a PTC composite, there is “METHOD OF MANUFACTURING POLYMER PTC FIXED-TEMPERATURE HEATING INK” (Korean Registered Patent Publication No. 10-1225759, Patent Literature 2), in which polyester-based and polyolefin-based resin is used as a binder, and a multi-walled carbon nanotube is used as a conductive filler, but there is a disadvantage that an organic solvent harmful for environments and human bodies such as toluene and xylene is used as a solvent.
In addition, as a conventional technique about a method of manufacturing a planar PTC element, there is “CONDUCTIVE COMPOSITE FOR MANUFACTURING HIGH-TEMPERATURE PLANAR PTC ELEMENT, HIGH-TEMPERATURE PLANAR PTC ELEMENT USING THE SAME, MANUFACTURING METHOD THEREOF” (Korean Laid-Open Patent Publication No. 10-2005-0109634, Patent Literature 3), but a manufacturing process is complicated such as forming and hardening a conductive composite formed of a mixture of a silicon sealant, a conductive filler, a coupling agent, and a reinforcement, to be a desired form.
As a conventional technique of manufacturing a heating element using a PTC element, there are “CONDUCTIVE COMPOSITE FOR MANUFACTURING CARBON FLEXIBLE HEATING STRUCTURE, CARBON FLEXIBLE HEATING STRUCTURE USING THE SAME, AND MANUFACTURING METHOD THEREOF” (Korean Registered Patent Publication No. 10-0535175, Patent Literature 4) and “CURRENT CONTROL RESISTANCE HEATING COMPOSITE MATERIAL AND MANUFACTURING METHOD OF PTC HEATING ELEMENT USING COMPOSITE MATERIAL” (Korean Laid-Open Patent Publication No. 10-2005-0114005, Patent Literature 5), a manufacturing process is complicated such as hardening after forming in a desired shape.
In addition, as a conventional technique of manufacturing a heating element using a PTC element, in “MANUFACTURING METHOD OF PTC FLEXIBLE PLANAR HEATING ELEMENT USING URETHANE-BASED THERMOPLASTIC ELASTOMER MATERIAL” (Korean Laid-Open Patent Publication No. 10-2011-0104247, Patent Literature 6), a method of forming a heating portion by drying after screen-printing a polymer-type conductive carbon black paste on an urethane-based thermoplastic elastomer sheet surface in a form of a plurality of horizontal lines is disclosed. As the polymer-type conductive carbon black paste is manufactured by dissolving polyurethane-based resin in a methyl ethyl ketone solvent and using barium ferrite as a conductive filler, there is a disadvantage of using an organic solvent.